Mr. Trump, who has made repairing strained ties with Moscow a central ambition of his presidency, even amid criticism of Russian meddling in last year’s American election, found that goal at risk as the countries traded harsh words in a diplomatic confrontation reminiscent of past dark moments between the two powers.

President Vladimir V. Putin’s office called the Tomahawk cruise missile strike on Syria a violation of international law and a “significant blow” to the Russian-American relationship, while Prime Minister Dmitri A. Medvedev said it had “completely ruined” it. Trump administration officials suggested Russia bore some responsibility for the chemical weapons attack on Syrian civilians that precipitated the American response.

At home, Mr. Trump found support among a broad cross-section of normally critical establishment Republicans and Democrats, including Hillary Clinton and Senator John McCain, who backed the sort of action that President Barack Obama refused to take under similar circumstances four years ago. Mr. Trump was among those who urged Mr. Obama not to order a strike back then, even though many more civilians had been killed at the time.

But in a sign of the complicated nature of domestic politics after nearly 16 years of American wars abroad, an odd-bedfellow mix of ideological enemies joined together to criticize Mr. Trump’s action, including antiwar liberals who said it violated the Constitution and isolationist conservatives who called it a betrayal of the values he expressed as a candidate. Even some who supported his action, like Mrs. Clinton, called Mr. Trump hypocritical for lamenting the deaths of Syrian babies while seeking to bar Syrian refugees from the United States.

The strike also roiled world capitals and dominated a session of the United Nations. Led by Russia, Syria and its backers denounced it, while American allies in Europe and in Israel, Turkey and Saudi Arabia cheered Mr. Trump on. The debate raged as the president was in Florida hosting a high-stakes summit meeting with President Xi Jinping of China to discuss, among other things, how to contain another international pariah state, North Korea.

Mr. Trump left it to others to address the issue on Friday, but his team signaled that no further military strikes were imminent unless the government of President Bashar al-Assad again used chemical weapons against Syria’s people.

“The United States took a very measured step last night,” Nikki R. Haley, the United States ambassador to the United Nations, said Friday during a special meeting of the Security Council focused on Syria. “We are prepared to do more, but we hope that will not be necessary.”

Even as Mr. Trump ordered the first direct American attack on Syria’s government in six years of grinding civil war, the White House indicated no further move to unseat Mr. Assad, leaving the strike to speak for itself. “This action was very decisive, justified and proportional,” said Sean Spicer, the president’s press secretary. “It sent a very strong signal not just to Syria, but throughout the world.”

Secretary of State Rex W. Tillerson characterized the strike as an “overwhelming success” and said Americans should be proud of the “overpowering” force of the American military. Treasury Secretary Steven Mnuchin announced that the United States would impose additional sanctions on Syria, but he did not discuss the timing or targets.

But the strike inserted the United States, for a moment at least, into one of the world’s most intractable conflicts and demonstrated the potential dangers of Russian and American forces’ operating in proximity. As many as 100 Russian troops were believed to be stationed at the Syrian air base targeted on Thursday. An American official said the Russians on the ground had been given 60 to 90 minutes’ notice that the missiles were coming and had not been advised whether to take shelter or flee.

Although Russia did not deploy its air defense system in Syria against the American missiles, it flexed its military muscles after the attack. Moscow said it would bolster Syria’s air defenses, and the Russian news agency Tass reported that a frigate would enter the Mediterranean Sea on Friday and visit the logistics base at Tartus, a Syrian port.

The Russian military said it would shut down a hotline established to prevent accidental clashes in the skies over Syria. While the two sides used the channel earlier on Friday, Russian officials said it would be cut off at the end of the day. The United States and Russia have other ways to track each other’s aircraft and avoid collisions, but American officials considered the hotline an important vehicle to ensure safety, as well as a valuable political connection.

Even as Moscow protested, American officials pointed fingers back, faulting the Kremlin for not enforcing a 2013 agreement it brokered with Syria to eliminate its chemical weapons. “Clearly, Russia has failed in its responsibility to deliver on that commitment from 2013,” Mr. Tillerson said late Thursday night. “So either Russia has been complicit or Russia has been simply incompetent in its ability to deliver on its end of that agreement.”

Russia, which sent armed forces to Syria in 2015 to bolster Mr. Assad against insurgents, denied that his government was behind the chemical attack on Tuesday in Idlib Province that left more than 80 people dead, calling that a pretext. Instead, Moscow said a conventional strike had hit a chemical weapons warehouse controlled by insurgents, an explanation dismissed in the West.

“The Syrian Army has no chemical weapons at its disposal,” said Dmitri S. Peskov, a spokesman for Mr. Putin, blaming “terrorists” for the attack.

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President Trump retaliated against the Assad government for a chemical attack in Syria that killed more than 80 civilians.CreditCreditFord Williams/U.S. Navy

Syria condemned the American strike as “a disgraceful act,” news agencies reported. A statement from Mr. Assad’s office said the cruise missile strike was a result of “a false propaganda campaign.” Syria has denied that it has chemical weapons.

The cruise missiles struck Al Shayrat airfield at 3:40 a.m. Friday local time (8:40 p.m. Thursday in Washington), targeting the base that American officials said had conducted the chemical weapons attack. The missiles were aimed at Syrian aircraft, hardened aircraft shelters, radars, air defense systems, ammunition bunkers and fuel storage sites. American military planners avoided sites that they suspected held chemical agents, officials said.

Syrian officials and news outlets reported that six soldiers and nine civilians had been killed. Talal Barazi, the governor of Homs Province, said the civilians had died from shrapnel wounds.

American military officials said 59 Tomahawk cruise missiles had struck their targets at the airfield, destroying 20 to 25 aircraft: roughly 20 percent of the Seventh Wing of the Syrian Air Force. One missile aborted after launch and fell into the Mediterranean.

But a spokesman for the Russian military, Maj. Gen. Igor Konashenkov, called the effectiveness of the American airstrikes “extremely low,” asserting that just 23 had hit their targets. The American missiles, according to the Russian military, destroyed a warehouse of matériel and technical property, a training building, a canteen, six MIG-23 aircraft in repair hangars, and a radar station. Evgeny Poddubny, a Russian television reporter who was at the air base, said nine planes had been destroyed.

The strike plan was put together at the United States Central Command in Tampa, Fla., and alternatives were developed within hours of the chemical attack. When Defense Secretary Jim Mattis briefed Mr. Trump on Thursday, the options had already been winnowed to a Tomahawk cruise missile strike at Al Shayrat.

Two American destroyers, the Porter and the Ross, were already in position in the eastern Mediterranean. Mr. Trump gave the order on Thursday afternoon, shortly before hosting Mr. Xi for dinner, and confided in the Chinese leader only as the meal was breaking up, aides said.

The presence of Russian military personnel at the airfield complicated the decision. Given the Russians’ presence, American officials said they must have known about or turned a blind eye to the Syrian chemical weapons. The United States notified the Russian forces on the ground in a conversation described as lengthy, with the Russians doing much of the talking. The Russians were at a part of the base that was not struck, Pentagon officials said.

The chemical assault on Tuesday struck the town of Khan Sheikhoun with what Turkey has identified as sarin, a banned nerve agent. American officials said intelligence agencies had monitored the attack, mapping the radar tracks showing Syrian warplanes leaving and returning to the base.

The attack killed 84 people, and 546 others were injured, Tarik Jasarevic, a spokesman for the World Health Organization, told reporters in Geneva, citing health officials in Idlib Province.

United Nations officials said heavy fighting in other parts of Syria had killed hundreds more civilians. Bombings in Idlib and Raqqa Provinces in recent weeks, including by a United States-led coalition, were the most intensive recorded in the Syrian conflict, said Ravina Shamdasani, a spokeswoman for the United Nations’ human rights office.

More than 130 civilians were killed and 170 injured in the same month in Raqqa, the center of the Islamic State — the vast majority in coalition airstrikes, Ms. Shamdasani said. Syrian government airstrikes conducted over two days in early April on Eastern Ghouta, a suburb of the capital, Damascus, killed at least 42 civilians, she added.

In the hours after the American missile strike, Iran — Russia’s main ally in the region in helping Mr. Assad — condemned it as “dangerous, destructive and a violation of international law.” But Britain expressed support, as did Chancellor Angela Merkel of Germany and President François Hollande of France, who issued a joint statement saying that Mr. Assad “bears sole responsibility.”

A spokesman for Turkey’s government said the American strike had been a positive response to “war crimes” in Syria, while a Saudi official praised the “courageous decision” by Mr. Trump. Prime Minister Benjamin Netanyahu of Israel said he hoped it would “resonate not only in Damascus, but in Tehran, Pyongyang and elsewhere.”

Clues to how Moscow will respond might not come until Tuesday, when Mr. Tillerson, the former chief executive of Exxon Mobil and an old friend of the Kremlin, is set to make his first visit to Russia as secretary of state.

“There will be many screams on the Russian television with people condemning the strikes, but everybody understands that this is just a symbolic act meant for Trump to look different from Obama,” said Vladimir Frolov, a foreign affairs analyst. “There won’t be any tangible reaction; this was a one-off strike.”

Others suggested that the lack of an initial Russian military reaction in Syria pointed to a realistic approach. “Moscow might not like Washington’s response,” Mark Galeotti, an expert on the Russian military, wrote in an online commentary, “but nor was it willing to stand in the way of it.”